The present invention relates to a recording medium supplying apparatus having a raised central region for preventing a recording medium from skewing as the medium is fed.
The above described apparatus is used for supplying a recording medium such as a sheet having a predetermined size to a register unit arranged in front of a printing unit in a copying machine or facsimile apparatus.
FIG. 8 schematically shows a structure of the conventional apparatus of the above described kind. As shown in FIG. 8, the conventional apparatus comprises a recording medium sending-out unit 10 for sending out a paper sheet P, and a recording medium transfer guide unit 16 for guiding the sheet P sent out from the sending-out unit 10 to a register unit 14 arranged in front of a printing unit 12. In the conventional apparatus of FIG. 8, the register unit 14 is structured by a pair of register rollers 14a.
The recording medium sending-out unit 10 comprises a recording medium cassette 10a containing a plurality of sheets P in a stacked state, a pickup roller 10b contacting an upper surface of an uppermost sheet P in the plurality of the sheets in the cassette 10a at a position near an inlet opening of the recording medium transfer guide unit 16 and selectively moving the uppermost sheet P toward the inlet opening, and a sending-out roller 10c for sending out the uppermost sheet P moved toward the inlet opening by the pickup roller 10b, into the recording medium transfer guide unit 16 through the inlet opening.
The recording medium transfer guide unit 16 includes a pair of guide members 16a and 16b which face each other with a gap much larger than the thickness of the sheet P. The guide member 16a has a portion constantly and slidingly contacting the sheet P to guide the transfer of the sheet P. A sliding contact surface of the portion of the guide member 16a has a comb-teeth like cross section as shown in FIG. 9 in order to reduce a sliding friction generating between the sliding contact surface and the sheet P. Projecting end surfaces of the ribs 18, the ribs 18 structuring the sliding contact surface of the comb-teeth like cross section of the guide member 16a, are placed on the same plane so that all of the projecting end surfaces of the ribs 18 covered by the sheet P slidingly contacting the sliding contact surface of the guide member 16a contact the sheet P.
The register unit 14 is arranged near an outlet of the recording medium transfer guide unit 16, and a length of a sheet transferring passage from the sending-out roller 10c to the register unit 14 via the recording medium transfer guide unit 16 is shorter than a length of the sheet P measured in its moving direction.
The sheet P discharged from the outlet of the recording medium transfer guide unit 16 abuts its leading end on a contact line between the paired register rollers 14a, 14a of the register unit 14. If the sheet P skews at this time with regard to the contact line as shown in FIG. 10, a moment M will be produced in the sheet P which is applied with a moving force F by the sending-out roller 10c, to turn the sheet P around at one corner L of the leading end contacting the contact line and to move another corner R of the leading end not contacting the contact line toward the contact line.
Whether the sheet P skews or not, the register unit 14 is driven to send out the sheet P toward the printing unit 12 after a sufficient time for correcting the skew of the sheet P has passed from a time when the sheet P is sent out from the cassette 10a. The printing unit 12 prints an image on the sheet P reached thereto on the basis of printing information supplied to the printing unit 12 in advance.
Even after the leading end of the sheet P has reached the contact line between the paired register rollers 14a, 14b of the register unit 14, the sheet P is still applied with the moving force F by the sending-out roller 10c, and thus the sheet P is bent due to the moving force F. The bend may easily occur, particularly in a portion at which the moving direction of the sheet P is changed in the sheet transferring passage in the recording medium transfer guide unit 16, i.e., in a bending portion of the transfer guide unit 16. A peak of the bend is strongly pushed against the projecting end surfaces of the ribs 18 of the guide member 16a. The bend of the sheet P is shown in FIG. 8 by a dotted line.
In the conventional apparatus structured as described above, the friction produced between the sheet P and each of the projecting end surfaces of the ribs 18 is substantially equal to each other. Therefore, if the sheet P skews, a turn of the sheet P for correcting the skew of the sheet P cannot be easily generated because the peak of the bend is strongly pushed against the projecting end surfaces bf the ribs 18 of the guide member 16a.
As a result of this, the sheet P may be supplied to the printing unit 12 without the skew of the sheet P being corrected by the register unit 14, so that an image may be printed on the sheet P in a wrong position or wrinkles of the sheet P may be generated in the sheet P, the wrinkles being able to clog the sheet P in the sheet transferring passage.